*{
    margin: 0;
    padding: 0;
    list-style-type: none;
}
.app{
    display: flex;
    width: 100vw;
    height: 100vh;
}
.left{
    width: 100px;
    border-right: 1px solid lightblue;
    height: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
}
.left>li{
    height: 50px;
    line-height: 50px;
    text-align: center;
    width: 100%;
}
.left>li>a{
    width: 100%;
    height: 100%;
    display: block;
}
.active{
    background-color: lightblue;
}